發(fā)布時間：2018-04-12 20:25

  本文選題：氮摻雜介孔碳材料 + 多功能載體�。� 參考：《催化學(xué)報》2017年07期

【摘要】：氮摻雜有序介孔碳材料不僅具有高的比表面積、大的孔容和均一可調(diào)的孔徑等優(yōu)點,其骨架中豐富的氮原子還可以對材料的物理化學(xué)性質(zhì)、配位金屬電荷密度等進行調(diào)控,是一類優(yōu)異的催化劑載體.本文利用軟模板(嵌段共聚物F127為模板),以間氨基苯酚為碳源和氮前體,制備出較高含氮量(9.58 wt%)和比表面積(417 m~2/g),以及規(guī)則孔徑分布的介孔碳材料.結(jié)果表明,制備的材料具有三維立方相結(jié)構(gòu).以該碳材料作為載體,使用傳統(tǒng)浸漬氫氣還原的策略負載納米鉑顆粒.發(fā)現(xiàn)氮摻雜的載體能夠有效控制金屬納米顆粒的尺寸,可實現(xiàn)超小尺寸Pt納米顆粒的有效負載(1.0±0.5 nm),且納米顆粒均勻分布于介孔碳材料的孔道中.相比而言,使用相同負載方法的情況下,以不摻氮的介孔碳材料為載體,納米粒子的尺寸較難控制(4.4±1.7 nm)且會發(fā)生孔道外顆粒聚集的情況.研究表明,骨架中的氮原子與金屬間弱的相互作用對納米粒子有穩(wěn)定作用.這對制備超小尺寸的金屬納米粒子催化劑具有一定的指導(dǎo)意義.此外,由于納米粒子的尺寸將大大影響催化劑活性中心的暴露程度,進而影響催化劑活性.因此,我們以硝基苯類化合物的氫化反應(yīng)來評價該催化劑的催化性能.在室溫和1 MPaH_2的溫和條件下,氮摻雜的介孔碳負載催化劑表現(xiàn)出了優(yōu)異的催化性能.反應(yīng)0.5 h,對氯硝基苯可完全轉(zhuǎn)化,且選擇性高達99%.相比而言,商業(yè)化的Pt/C催化劑上反應(yīng)的轉(zhuǎn)化率和選擇性分別為89%和90%.其它傳統(tǒng)催化劑的比較,如Pt/SiO_2,Pt/TiO_2,同樣表明,氮摻雜介孔碳負載的催化劑具有更優(yōu)異的催化性能.在相同反應(yīng)條件下,Pt/SiO_2催化劑只能得到46%的轉(zhuǎn)化率和93%的選擇性,而Pt/TiO_2催化劑雖然能夠?qū)崿F(xiàn)完全轉(zhuǎn)化,但選擇性也僅為91%.由此可見,氮摻雜的負載催化劑可大大提高反應(yīng)活性和選擇性,能有效抑制脫氯現(xiàn)象的發(fā)生.這種高的催化性能可能與催化劑的介孔結(jié)構(gòu)、氮功能化載體以及超小尺寸的Pt納米粒子的穩(wěn)定有關(guān).由于氮原子和介孔孔道的限域作用,氮摻雜介孔碳負載的催化劑也具有良好的催化穩(wěn)定性,循環(huán)使用10次后,催化活性和選擇性幾乎沒有下降.結(jié)果表明,循環(huán)使用后的催化劑金屬粒子尺寸變化不大,進一步表明氮摻雜介孔碳載體對金屬納米顆粒的穩(wěn)定作用.
[Abstract]:Nitrogen-doped ordered mesoporous carbon materials not only have the advantages of high specific surface area, large pore volume and uniform and adjustable pore size, but also can regulate the physical and chemical properties of materials and the charge density of coordination metals.It is a kind of excellent catalyst support.In this paper, a soft template (block copolymer F127 as template, m-aminophenol as carbon source and nitrogen precursor) and a specific surface area of 417mg / g, as well as regular pore size distribution mesoporous carbon materials were prepared.The results show that the prepared material has three dimensional cubic phase structure.Using the carbon material as the carrier, the traditional impregnated hydrogen reduction strategy was used to load the platinum nanoparticles.It is found that the nitrogen-doped carrier can effectively control the size of metal nanoparticles and realize the effective loading of ultra-small Pt nanoparticles (1.0 鹵0.5 nm), and the nanoparticles are uniformly distributed in the pores of mesoporous carbon materials.In contrast, under the same loading method, it is difficult to control the size of nanoparticles by using nitrogen-free mesoporous carbon materials as the carrier, and the accumulation of particles outside the channels will occur.The results show that the weak interaction between nitrogen atoms and metals in the skeleton has a stable effect on the nanoparticles.It has certain guiding significance for the preparation of ultrasmall metal nanoparticles catalyst.In addition, the size of nanoparticles will greatly affect the exposure of the catalyst active center, and then affect the activity of the catalyst.Therefore, the hydrogenation of nitrobenzene compounds was used to evaluate the catalytic performance of the catalyst.The nitrogen-doped mesoporous carbon supported catalysts exhibited excellent catalytic performance at room temperature and 1 MPaH_2.After 0.5 h reaction, p-chloronitrobenzene could be transformed completely, and the selectivity was as high as 99wt%.In contrast, the conversion and selectivity of the commercial Pt/C catalyst were 89% and 90%, respectively.The comparison of other traditional catalysts, such as PT / SiO2 / PtP / TiO2, also shows that nitrogen-doped mesoporous carbon supported catalysts have better catalytic performance.Under the same reaction conditions, only 46% conversion and 93% selectivity can be obtained for Pt- SiO2 catalyst, while Pt/TiO_2 catalyst can achieve complete conversion, but the selectivity is only 91%.It can be seen that nitrogen-doped supported catalysts can greatly improve the activity and selectivity of the reaction, and can effectively inhibit the phenomenon of dechlorination.The high catalytic performance may be related to the mesoporous structure of the catalyst, the nitrogen functionalized support and the stability of the ultrasmall Pt nanoparticles.Because of the limiting effect of nitrogen atom and mesoporous channel, the catalyst supported by nitrogen doped with mesoporous carbon also has good catalytic stability. After 10 cycles, the catalytic activity and selectivity are almost unchanged.The results showed that the size of catalyst metal particles changed little after recycling, which further indicated the stability of nitrogen-doped mesoporous carbon support on metal nanoparticles.
【作者單位】： 山西大學(xué)分子科學(xué)研究所;山西大學(xué)化學(xué)化工學(xué)院;
【基金】：supported by the National Natural Science Foundation of China(201573136,U1510105) the Scientific Research Start-up Funds of Shanxi University(RSC723)~~
【分類號】：O643.36

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